Industrial gas consumers frequently request a relatively tight control in pressure variations of pressurized gas produced from a gas production facility. It is desirable that pressure variations remain within these relatively tight limits regardless of disruptive events that inevitably occur at the industrial facility, at least upon occasion. For example, such events may include stopping operation of the air separation unit for scheduled as well as non-scheduled plant shutdowns.
Similarly, it is also optimal to other users of pressurized gas to minimize pressure variations and to maintain the pressures in a desired range.
In modern air separation units, internal compression processes may be utilized to directly obtain gases under pressure at the cold box outlet. The liquefied gas is extracted from a distillation column, a separator, or a vessel. The liquefied gas may then be compressed by a pump and vaporized under pressure to produce high-pressure gaseous product, e.g., high-pressure gaseous oxygen.
When the normal production of gaseous products stops for any cause such as, for instance, purity upset, scheduled or non-scheduled shutdowns, or other reasons, the delivery of the gaseous products may be maintained by a backup system that may include one or more liquid storage tanks, pumps, and a backup vaporizer of various types. The switch over from normal mode to the backup mode has, in the prior art, generally produced a pressure fluctuation of the gaseous product in the pipeline connecting the air separation unit to the consumers.
To satisfy the customer requests regarding pressure fluctuations, mainly during air separation unit upset or shutdown, several possible solutions have been proposed. Each solution has advantages, but also has significant disadvantages.
One solution would provide a high-pressure gaseous buffer tank installed down stream of the back-up vaporizer. This method provides a very fast response time, but is a capital-intensive solution.
Another proposed solution would involve providing a high-pressure liquid tank installed upstream of the backup vaporizer. This solution provides a relatively fast response time, but is also capital intensive and is limited in the range of operating pressure permitted by this solution.
Another proposed solution would involve running a backup vaporization pump at an extremely reduced rate to minimize the start-up time of the backup pump, and the vaporizer. This method has a very fast response time, but it is liquid and energy consuming.
Consequently, improved systems and method are needed to minimize pressure fluctuations that occur during air separation unit upset or shutdown while simultaneously considerably reducing the capital investment required to effect such systems and methods. It would be desirable to have a simpler system, that is low in energy consumption, useable at all operating pressures, and which has a very fast response time. Those of skill in the art will appreciate the present invention that addresses the above and other problems.